This invention relates to tapered block copolymers of conjugated dienes and monovinylarenes.
In another aspect, this invention relates to a method of preparing tapered block copolymers of conjugated dienes and monovinylarenes.
There has developed in the polymer field, and especially in the packaging and related industries, a need for thermoplastic polymers that can be formed into transparent articles having high impact strength with good environmental stress crack resistance. These should be suitable for use with conventional injection and blow molding equipment and also suitable for use in other methods of forming plastics into containers, tubes, films, fibers, and the like. Polystyrene, high impact polystyrene, branched block copolymers, and the like have been developed to meet these criteria with various degrees of satisfaction.
Much effort has been directed to the preparation of substantially transparent block copolymer resins with a variety of block structures produced by a variety of monomer addition sequences and a variety of coupling agents.
Polymerization of styrene and butadiene with organolithium initiators to produce block copolymers in which one or more non-elastomeric polymer blocks are bonded to one or more elastomeric polymer blocks has been disclosed. Similarly, styrene-butadiene block copolymers with tapered blocks have been prepared by sequential charging of initiator and monomers to the polymerization zone. Block copolymers have been formed by sequential charges of the monomers followed by introduction of one or more coupling agents into the reaction.
Literally thousands of various combinations of sequences of charges of monomers and coupling agents are possible.